Backbone-Degradable Acrylate Latex: Toward Overcoming Hydrolysis Limitations of Cyclic Ketene Acetal Monomers

Latex particles made with radical emulsion polymerization contain all carbon-backbone polymer chains, which are nonhydrolyzable and nonbiodegradable in the environment and hence pose a huge challenge as persistent pollutants. Radical ring-opening copolymerization (rROP) of cyclic ketene acetals (CKAs) such as 2-methylene-1,3-dioxepane (MDO) with vinyl monomers is an interesting approach being explored intensely for introducing degradable ester groups in the polymer backbones, opening up the potential of synthesizing biodegradable copolymers. However, carrying out such reactions in an aqueous medium to obtain biodegradable dispersions is very challenging due to the hydrolytic instability of CKAs. There are conflicting reports on preparing degradable lattices via rROP of MDO with vinyl acetate (VAc) monomers, but subsequent detailed reaction parameters were published, which show that under the right conditions, successful copolymerizations can be performed. We report that the use of neutral surfactants, high pH, and stabilizing comonomers play a crucial role in the successful incorporation of degradability in the polymer backbone during emulsion copolymerization. This is the first report on the synthesis of acrylate copolymers with the incorporation of hydrolytic degradability (utilizing MDO) under potentially more industrially feasible emulsion polymerization conditions. The findings underscore the potential for further improvement in this area. The results in the current study provide further insight into the breadth of parameters that must be carefully considered to produce biodegradable lattices via the rROP of CKAs.